Process for making high-strength,wettable aluminum foil



' April 15, 1969 R. H. ABERLE ET AL 3,438,228

PROCESS FOR MAKING HIGH-STRENGTH, WETTABLE ALUMINUM FOIL Filed May 14, 1965 T HEB/ 141. TREATMENT 77ME -H0l/25 Q 400F INVENTORS ,Q/c/mw 6. 1485245 205:2? h! Aums QOLL WIDTH IN INCHES 4 United States Patent 0 US. CI. 72-42 6 Claims ABSTRACT OF THE DISCLOSURE A process for producing high-strength, substantially fully work-hardened, 100% Water-wettable aluminum foil, comprising the steps of cold-rolling aluminum down to foil gauge, using a rolling oil of narrow distillation range, more than 90% of which has a boiling point below 550 F to which has been added minor amounts of butyl stearate and lauric acid; rewinding the foil into coils of uniform density not more than about 96% of the density of solid aluminum; and thermally treating the coil at about 400 F. for from one-half hour to two and onehalf hours per inch of coil width.

The present invention relates to high-strength, waterwettable aluminum foil for use by the converter industry in manufacturing laminated and/ or printed foil.

Laminated and/or printed aluminum foil is used in great quantities in packaging foods, tobacco products, pharmaceutical preparations, and many other products. There has long been need for a high strength foil that could withstand the stresses of printing and laminating at higher speeds than are possible with the normal, dead soft converter foil that has heretofore been commercially available. The difficulty is that converter foil must be 100% water wettable with distilled water, in order to make it take the inks or to adhere to plastic films. In order to make it water-wettable, foil coming off the final mill is heated to around 600 F. or higher, and held at that temperature for a number of hours, depending upon the width of the coil, to burn off the rolling oil and matting solvent that are left on the foil from the final tl'Oll pass. Prior to this thermal treatment, the foil is fully work-hardened and consequently has high strength, but it is non-wettable with distilled water because of the film of rolling oil and matting solvent on its surfaces, and therefore cannot be used by the converter industry. After the thermal treatment, the foil is clean and dry, and is 100% wettable with distilled water, but it is now fully annealed and dead soft, consequently low in strength.

The foil-producing industry has sought to minimize the annealing effect of the thermal treatment by reducing the temperature of the treating furnace to a level below the recrystallization temperature of the aluminum alloy, but efforts in this direction have been completely unsuccessful, and have been abandoned. Instead, the industry has sought to achieve the desirable end result of a highstrength, 100% water-wettable aluminum foil by going to high-strength alloys, such as the 5052 Series, which retain their strength even when fully annealed by the thermal cleaning process. However, the high-strength 5052 Series alloys are considerably more costly than the lower strength 1100 and 1145 alloys, of which most converter foil is made. Such high-strength alloy foils (of the 5052 Series, for example) sell at a premium price about 50% higher than the price of a corresponding gauge of foil in Type 1100 or 1145 alloy, and this premium price limits its use.

The primary object of the present invention is to provide a high-strength, substantially fully work-hardened,

3,438,228 Patented Apr. 15, 1969 100% water-wettable aluminum foil, using the lower strength alloys, such as the 1100 Series, which are not less than 99% aluminum, and not more than 1% total of alloying elements.

Another object of the invention is to produce a highstrength, 100% water-wettable aluminum foil which is no more costly to manufacture than conventional lowstrength converter foil.

A further object of the invention is to produce a highstrength, water-wettable foil of the class described, which unwinds completely freely from the coil. The rolling oils and matting solvents used in the rolling operation, if not completely removed, tend to act as a rather weak adhesive between adjoining layers of foil on a roll, with the result that the foil will not unwind freely. Ditficulties in unwinding are unually not serious when the web is being paid off at a low linear rate, but at high speeds any slightest tendency of the web to stick can result in jerky feeding and breakage of the web.

Another object of the invention is to provide a new and improved process for producing high-strength, substantially fully work-hardened, 100% water-wettable aluminum foil. More specifically, it is an object of the invention to provide a process for producing high-strength converter foil, using aluminum alloys of the 1100 Series, which are normally considered to be low-strength alloys.

These objects are achieved in the present invention by using special rolling oils having certain additives therein to cool and lubricate the rolls in the rolling operation, said rolling oils having a narrow and relatively low-temperature distillation range Well below the recrystallization temperature of the aluminum alloy. The foil is wound onto rolls of extremely uniform density of not more than about 96% of the density of solid aluminum, and the rolls are then thermally treated at a temperature well below the recrystallization temperature of the metal for a period of time that is a function of .roll width, until the rolling oil has been completely evaporated and has diffused out through the ends of the roll.

One very important requirement in the practice of the present invention is that the rolls of foil to be thermally treated must be uniform in density from the inside layer of foil to the outside layer, and this density should not be greater than about 96% of the theoretical maximum density (i.e., the density of solid aluminum). In order to achieve this uniform density of the roll, with a maximum density of not more than 96%, the doubled layers of foil that come off the final roll pass are rewound onto two separate rolls of one layer each, using ironing rolls that are pressed with uniform pressure against the outer surface of the foil on the rewind rolls. Hydraulic cylinders press the ironing rolls against the foil with uniform pressure from start to finish, with the result that the finished rolls are extremely uniform in density throughout.

Another important object of the invention, therefore, is to provide means for winding rolls of foil that are extremely uniform in density throughout, and in which the density of the roll does not exceed about 96% of theoretical maximum.

These and other objects and advantages of the invention will become apparent to those skilled in the art from the following detailed description, reference being had to the accompanying drawings, wherein:

FIGURE 1 is a schematic drawing, showing the final roll pass in the cold-rolling operation, wherein two superimposed layers of foil are rolled together;

FIGURE 2 is aonther schematic drawing, showing the two layers of foil being separated and rewound onto two separate rolls, and also showing the ironing rolls that press against the foil with uniform pressure from start to finish, to produce rolls of uniform density; and

FIGURE 3 is a chart showing the time and temperature required to thermally treat the rolls of foil to evaporate all of the rolling oil without annealing the foil.

In FIGURE 1, the reference numeral designates a 4-high rolling mill consisting of upper and lower work rolls 11 and 12, and back-up rolls 13 and 14. On one side of the mill 10 are two supply rolls 15 and 16, holding foil requiring one final roll pass to bring it down to the desired foil gauge.

Preferably, the foil used in the present invention is of the 1100 Series of aluminum alloys, using the designation of the Aluminum Association Standardized System. The alloy that we have had the most successful results with is designated Type 1100 alloy, which has the following composition:

Percent Silicon and iron (max) 1.00 Copper (max) 0.20 Manganese (max) 0.05 Zinc (max.) 0.10 Other elements, each (max.) 0.05 Other elements, total (max.) 0.15

Aluminum (min.) 99.00

This is a high-purity aluminum alloy of the type generally considered to be low-strength, although it does have the characteristics of work-hardening. After passing through the final mill 10, the foil is substantially fully work-hardened, and has a tensile strength of from 17,000 to 20,000 p.s.i., and a Mullen strength of between 3.5 and 4.25. These properties are to be compared to the tensile strength of 6,000 to 8,000 p.s.i., and Mullen strength of 1.8 to 2.5 for normal dead soft converter foil of the same alloy and gauge.

Foil from supply roll 15 is brought up over the top of roll 16 and is superimposed on the foil of roll 16. A supply pipe 20 with suitable spray nozzles provided thereon, extends across the space between rolls 15, 16, and sprays matting solvent onto the facing surfaces of the two webs of foil. The purpose of the matting solvent is to prevent the two webs of foil from pressure-welding together as they pass between the work rolls. A matting solvent suitable for this purpose is sold by Mobil Oil Company under the trademark Solvasol. From the top of supply roll 16, the two juxtaposed webs of foil pass over breaker rolls 22 and 24, through the work rolls 11, 12, over breaker roll 26, and are wound onto a common roll, or coil 28. The finished toil on roll 28 may be from .00025" to .00050" in thickness.

The rolls of the mill 10 are cooled and lubricated by means of rolling oil, which is sprayed onto the work rolls 11, 12 by two lines of spray nozzles 30 and 32. The rolling oil is a light oil of relatively narrow, low temperature distillation range, preferably in the range of 350 to 570 F. We have found that good results are obtained with the rolling oil marketed by the Shell Oil Co. under the trademark Shell Rollex 111 Oil. This is a water white oil of .848 specific gravity, having a viscosity of SSU at 100 F., and flash point of approximately 215 F. According to published specifications, more than 90% of all fractions of the Rollex 111 Oil have boiling points below 550 F.

The abovementioned rolling oil is primarily a coolant, and to this we add from 1 to 5% by weight of butyl stearate, and from 0.25 to 0.75% by weight of lauric acid. The butyl stearate and lauric acid serve primarily as loadbearing lubricants, as they readily withstand the extremely high unit pressures encountered between the work rolls 11 and 12.

The roll 28 of juxtaposed webs of foil is then removed to a separator and rewinder, shown in FIGURE 2. Here, the two webs are pulled 011 the roll 28 and are carried over rollers 34, 36, 38, and 42, and then pass upwardly between two side-by-side separator rolls 44 and 46. One of the webs of foil passes to the left, over the top of roll 44, and is wound onto a roll 48. The other web passes to the right, over the top of roll 46, and is wound onto roll 50.

Bearing against the bottom side of each of the rolls 48 and 50 is an ironing roll 52. The ironing rolls 52 are each rotatably supported betwen the free ends of pairs of lever arms 54 (only one of which can be seen in FIG. 2), and the other ends of the lever arms are pivoted for swinging movement about the axes of their respective rolls 44, 46.

The ironing ,rolls 52 are pressed upwardly against the undersides of rolls 48 and 50, by means of hydraulic cylinders 55 having piston rods 58. The piston rods 58 are connected by suitable pivot connections to the lever arms 54 about midway of their length, and the cylinders 56 are pivotally supported at 60. Fluid supply lines 62 carry hydraulic fluid from a pressure regulator 64 to the bottom ends of the cylinders 55, and by maintaining a constant pressure on the hydraulic fluid, the cylinders 56 are caused to hold the ironing rolls 5'2 against the rewind rolls 48, 50 with a constant pressure from the start of the roll to its finish.

By maintaining a tension of from 5000 p.s.i. to 7500 psi. in the two webs of foil being wound onto the rolls 48, 50, and by pressing the ironing rolls 52 against the rolls 48, 50 with a presure of about 20 to 25 pounds per inch of roll width, we obtain rolls of extremely uniform density, not more than 96% of the theoretical maximum, which would be the density of solid aluminum.

The rewind coils 48 and 50 are then placed in a thermal treatment oven Where they are held for a number of hours at a temperature well below the recrystallization temperature of the metal. For cold-rolled aluminum alloys of the 1100 Series having a substantial amount of cold-work (e.g., of the order of or more), the recrystallization temperaturei.e., the temperature at which recrystallization can be initiatedis approximately 500 F. With a lesser amount of cold-work, the recrystallization temperature of the metal is somewhat higher, in the range of 500 F. to 580 F. Thus, the 600 F. temperature to which foil has heretofore been heated to remove residual rolling oil and matting solvent, has been well above the recrystallization temperature of the aluminum alloy, and has resulted in fully annealed, dead soft foil, which does not have the necessary physical properties for certain uses in the converter industry. Preferably, the thermal treatment of the present invention is done at a temperature of 400 F., for a period of time ranging from about one-half hour to about two and one-half hours per inch of coil width. This 400 F. thermal treatment is well below the recrystallization temperature of the metal, yet, at the same time, well within the distillation range of the rolling oil. FIGURE 3 shows a typical time vs. roll width curve, with a treatment temperature of 400 F. The time per inch of roll width can be varied by using a rolling oil having a lower temperature distillation range, and could also be reduced by reducing the pressure within the treatment furnace.

By the end of the thermal treatment, the rolling oil and matting solvent have been completely evaporated, and have diffused out through the ends of the rolls. The thermal treatment temperature is well below the recrystallization temperature of the aluminum foil, and the foil therefore retains its full-hard temper. The finished foil is 100% wettable with distilled water, and unwinds completely free from the roll. A foil made in accordance with this invention to a gauge of .0003" has been fed unsupported through a four-color rotogravure press and printed one color plus over lacquer on one side and vinyl coated on the other. Unsupported .0003" gauge foil has been extrusion-coated with two-thirds of a mil of polyethylene, and in another instance, unsupported .0003 foil has been machine applied as a lid to TV dinners.

While we have shown and described in considerable detail what we believe to be the preferred form of our invention, it will be understood by those skilled in the art that various changes may be made without departing from the scope of the following claims.

We claim:

1. A process for producing high-strength, substantially fully work-hardened 100% water-wettable aluminum foil, comprising the following steps:

(a) cold rolling aluminum down to foil gauge, using rolling oil of relatively narrow, low-temperature distillation range, of the order of 350 to 570 F., to cool and lubricate the rolls;

(b) Winding the foil into a roll of uniform density of not more than about 96% of the density of solid aluminum; and

(c) heating the roll of foil to a temperature below the recrystallization temperature of the aluminum and holding it at said temperature for a period of time that is a function of the roll width, until said rolling oil has been completely evaporated and has diffused out through the ends of the roll without annealing the foil.

2. A process for producing high-strength, substantially fully work-hardened, 100% water-wettable alumi num foil, comprising the following steps:

(a) cold rolling aluminum down to foil gauge, including a final roll pass wherein two superimposed layers of foil are rolled together and are wound into a common coil;

(b) using rolling oil of relatively narrow and relatively low-temperature distillation range, of the order of 350 to 570 F., more than 90% of all fractions of said rolling oil having boiling points below 550 F.;

(c) rewinding the two layers of foil into separate rolls to a density of not more than about 96% of the density of solid aluminum, while maintaining a uniform density of the roll from its inner layer to its outer layer; and

(d) thermally treating said rewound rolls at a temperature well below the recrystallization temperature of the aluminum and for a period of time that is a function of the roll width, until said rolling oil has been completely evaporated and has diffused out through the ends of the roll, without annealing the foil.

3. A process for producing high-strength, substantially fully work-hardened, 100% water-wettable aluminum foil, comprising the following steps:

(a) cold rolling aluminum down to foil gauge, including a final roll pass wherein two superimposed layers of foil are rolled together and are wound onto a common roll;

(b) using a rolling oil of relatively narrow, lowtemperature distillation range of the order of 350 to 570 F. to cool and lubricate the rolls;

(c) rewinding the two layers of foil onto two separate coils while ironing the foil onto said two coils, using an ironing roll that is pressed against the outer surface of the coil with a uniform pressure from the start of the coil to its finish, thereby producing a coil of uniform density of not more than about 96% of the density of solid aluminum; and

(d) thermally treating said coils at a temperature well below the recrystallization temperature of the aluminum and for a period of time that is a function of the coil width, until said rolling oil has been completely evaporated and has diffused out through the ends of the coil, without annealing the foil.

4. A process for producing high-strength, substantially fully work-hardened, 100% water-wettable aluminum foil, comprising the following steps:

(a) cold rolling aluminum down to foil gauge, includ ing a final roll pass wherein two superimposed layers of foil are rolled together and are wound onto a common coil;

(b) using a rolling oil of relatively narrow, lowtemperature distillation range of the order of 350 to 570 F. to cool and lubricate the rolls;

(c) rewinding the two layers of foil onto two separate coils while ironing the foil onto said two coils, using an ironing roll that is pressed against the outer surface of the coil with a uniform pressure from the start of the coil to its finish, thereby producing a coil of uniform density of not more than about 96% of the density of solid aluminum; and

(d) thermally treating said coils at a temperature of about 400 F. and for a period of time ranging from about one-half hour to about two and one-half hours per inch of coil width, until said rolling oil has been completely evaporated and has diffused out through the ends of the coil, without annealing the foil.

5. A process for producing high-strength, substantially fully work-hardened, 100% water-wettable aluminum foil, comprising the following steps:

(a) cold-rolling aluminum down to foil gauge, including a final roll pass wherein two superimposed layers of foil are rolled together and are wound onto a common coil;

(b) using a rolling oil of narrow distillation range, more than of which has a boiling point below 550 F., to which has been added from 1% to 5% by weight of butyl stearate, and from 0.25% to 0.75% by weight of lauric acid;

(c) rewinding the two layers of foil onto two separate coils while ironing the foil onto said two coils, using an ironing roll that is pressed against the outer surface of the coil with a uniform pressure from the start of the coil to its finish, threby producing a coil of uniform density of not more than about 96% of the density of solid aluminum; and

(d) thermally treating said coils at a temperature of about 400 F. and for a period of time ranging from about one-half hour to about two and one-half hours per inch of coil width, until said rolling oil has been completely evaporated and [has diffused out through the ends of the coil, without annealing the foil.

6. A process for producing high-strength, substantially fully workhardened, 100% water-wettable aluminum foil, comprising the following steps:

(a) cold rolling aluminum down to foil gauge, using rolling oil of relatively narrow, low-temperature distillation range, of the order of 350 to 570 F., to cool and lubricate the rolls;

(b) winding the foil into a roll of uniform density of not more than about 96% of the density of solid aluminum; and

(c) thermally treating said coil at a temperature of about 400 F. and for a period of time ranging from about one-half hour to about two and one-half hours per inch of coil width, until said rolling oil has been completely evaporated and has diffused out through the ends of the coil, without annealing the foil.

References Cited UNITED STATES PATENTS 229,676 7/1880 Crooke 2918 1,225,044 5/1917 Lauber et al 29-18 1,887,248 11/1932 Shover 2918 3,169,300 2/1965 Nagle et al 29--18 RICHARD J. HERBST, Primary Examiner.

US. Cl. X.R. 

